1. Field of the Invention
The present invention relates to a fuel rod testing apparatus for a nuclear fuel assembly and, more particularly, to a fuel rod testing apparatus for effectively performing a helium leakage test and macrography on a fuel rod that is finally assembled as a unit part in the process of manufacturing the fuel rod.
2. Description of the Related Art
Nuclear reactors are facilities for artificially controlling a fission chain reaction of a fissionable material in order to use thermal energy generated from nuclear fission as power.
Referring to FIG. 1, a nuclear fuel assembly includes spacer grids 2 into which fuel rods are inserted, numerous guide thimbles 3 fixed to the spacer grids 2, an upper end fitting 3 fastened to upper ends of the guide thimbles 2, and a lower end fitting 4 fastened to lower ends of the guide thimbles 2. Each fuel rod is supported by dimples and springs formed on each spacer grid 2.
The fuel rod is made up of a cladding tube, end plugs, pellets, and springs. The fuel rod is manufactured by enriching uranium-235 of 2 to 5% to form a cylindrical nuclear fuel pellet of about 5 g, charging the pellets into the cladding tube, inserting the springs, and sealing the cladding tube using the end plugs.
In the process of charging and sealing the pellets into the cladding tube, the cladding tube is filled with an inert gas such as pressurized helium, thereby reducing and preventing oxidation of the pellets.
For example, a nuclear fuel rod having a structure capable of being effectively filled with helium is proposed in Korean Unexamined Patent Application Publication Nos. 10-2006-0134959 (published on Dec. 28, 2006) and 10-1988-0004492 (published on Jun. 4, 1988).
In this way, helium introduced into the fuel rod under pressure can reduce or prevent the oxidation of the pellets. Especially, the helium introduced under pressure in the fuel rod for a pressurized water reactor (PWR) functions to relieve compressive stress and creep of the cladding tube, which are generated due to pressure of external cooling water.
Thus, a process of testing for leakage of the helium after the fuel rod has been manufactured is required.
In regard to this, a method and apparatus for testing for leakage of helium from a nuclear fuel rod are proposed in Korean Unexamined Patent Application Publication Nos. 10-1990-0012289 (published on Aug. 3, 1990). Referring to FIG. 2, the apparatus for testing for leakage of helium from a nuclear fuel rod is provided with a testing chamber 16 having a sealed structure in which it is tested whether or not the helium leaks from the nuclear fuel rod, a first conveyer 36 disposed at one end of the testing chamber 16 to convey the fuel rod to be tested, a second conveyer 38 disposed inside the testing chamber 16, and a third conveyer 40 disposed at the other end of the testing chamber 16 to convey the tested fuel rod.
In the helium leakage testing apparatus, the fuel rod is conveyed by the first conveyer 36. Another fuel rod waits for testing outside the testing chamber 16. The fuel rods tested in the testing chamber 16 are discharged to the outside of the testing chamber 16 by the second conveyer 38 installed inside the testing chamber 16 and the third conveyer 40. The discharged fuel rods are transferred to the next process by a transfer line.
The fuel rods have a length of about four meters and are conveyed in a horizontal direction. For these reasons, to transfer the fuel rods to the next process in the testing chamber using the conveyer, a long transfer line is required, and thus a wide space for facilities is required. Consequently, efficiency of the process is reduced.